The present invention relates to a data processing technique and a technique suitably applicable to processing to code and to decode digital data using an encryption key code, for example, to a technique efficiently applicable to a communicating semiconductor device and a system using the device in which data is communicated between electronic apparatuses connected to each other via a serial bus conforming to, for example, the standard of Institute of Electrical and Electronics Engineers 1394 (IEEE1394) while guaranteeing safety of the communication.
The IEEE1394 standard is a standard to serially transmit digital data of audio and video information between electronic apparatuses such as audiovisual (AV) apparatuses via a cable. Recently, there have been proposed electronic apparatuses in which electronic apparatuses such as an integrated receiver decoder (IRD), a digital video home system (D-VHS), and a digital video (DV) camera recorder (camcoder) are connected to each other via a serial bus of the IEEE1394 standard to communicate digital contents including, for example, digital audio data and/or digital video data therebetween using a packet conforming to, for example, the Moving Picture Experts Group 2 Transport Stream (MPEG2-TS) according to the International standardization Organization/International Electrotechnical Commission (ISO/IEC) 13813 standard and a packet conforming to the IEC61883 standard.
For media such as a digital video tape and a digital video disk to store copyrighted materials such as a film and reproducing apparatuses to reproduce the materials, a technique to prevent illegal copying of the copyrighted material is indispensable in consideration of protection of copyrights. Recently, to protect copyrights of digital contents, an illegal copy prevention technique is being standardized, for example, by a copy protection technical working group (CPTWG) organized by industrial groups organized by the industry for the electric appliance for family use, personal computers, and films. According to an illegal copy protection technique proposed primarily by CPTWG, a specification of content scrambling system (CSS) of DVD video and a specification of 5 company digital transmission content protection (5C-DTCP) for IEEE1394 have been put to practices at present.
However, against CSS of the DVD-video copy protection technique, some crackers, i.e., hackers who illegally access computer systems of other person for malicious purposes have already created software to circumvent or to break security provided by CSS. In the U.S.A. and France, the software has been delivered via the internet through worldwide web (www) servers and has caused damages in various fields of the industry.
Therefore, in a situation in which a large amount of audiovisual apparatuses using an identical security technique such as the standardized CSS or 5C-DTCP are widely spread in the world, highly reliable security is necessary for the audiovisual apparatuses against illegal copy by crackers in consideration of the protection of copyrights for digital contents.
As a vicious example of the illegal copying of copyrighted materials, an illegal or an authorized game machine has been put to market. The illegal game machine is implemented by illegally modifying hardware of a game machine of a known company to enable the illegal copying of game software stored on a compact disk (CD). The copyright of the game software has been infringed. As above, in the present stage of technique, there possibly occurs software wise and hardware wise attack, that is, not only the illegal copy by software but also the illegal copy by modified hardware of electronic apparatuses are used to attack the illegal copy protection technique.
On the other hand, 5C-DTCP has been practically applied to a system below. FIG. 13 shows a general configuration of an audiovisual apparatus as an authentication communicating apparatus of the 5C-DTCP specification and a system using the apparatus according to the prior art. The configuration of FIG. 13 includes a communicating semiconductor device (communicating apparatus) 72 of the 5C-DTCP specification and an authentication device 71 including a microcomputer chip to conduct authentication. The authentication device 71 and the communicating device 72 are mounted on audiovisual apparatuses such as a digital video tape recorder and a set-top box.
As shown in FIG. 13, the communicating device 72 includes a low-layer interface circuit 100 to establish connections to IEEE1394 serial buses 741 to 743, an upper-layer interface circuit 200 to establish a connection to an external device, and an encryption circuit 300. The communicating device 72 is connected between a 1394 physical (PHY) layer as a physical layer including ports 711 to 713 to establish connections to cables 730 of the IEEE1394 standard and an external device 90 such as a display including an MPEG2 decoder, a codec, or a DV codec. The communication device 72 has a function which receives encrypted digital data from the IEEE1394 cable 730 to decode the digital data to pass the decoded digital data to the external device 80. The low-layer interface circuit 100, the upper-layer interface circuit 200, and the encryption circuit 300 may be configured as respectively separate chips depending on cases. The authentication device 71 is connected via an internal bus 41 to the communicating device 72. The authentication device 71 has a function to generate an encryption key code (to be simply referred to as an encryption key herebelow) necessary for the encryption circuit 300 and a function to conduct authentication in response to a request from an audiovisual apparatus which desires to receive data.